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1. Transformer Coupled Toroidal Wave-Heated Remote Plasma Sources Operating in in Ar/NF ₃ Mixtures

   https://doi.org/10.1088/1361-6463/ad660f  

   Doyle, Scott James; Larson, Amanda; Rosenzweig, Guy; Gunn, James; Kushner, Mark J (July 2024, Journal of Physics D: Applied Physics)

   Abstract Remote plasmas are used in semiconductor device manufacturing as sources of radicals for chamber cleaning and isotropic etching. In these applications, large fluxes of neutral radicals (e.g., F, O, Cl, H) are desired with there being negligible fluxes of potentially damaging ions and photons. One remote plasma source (RPS) design employs toroidal, transformer coupling using ferrite cores to dissociate high flows of moderately high pressure (up to several Torr) electronegative gases. In this paper, results are discussed from a computational investigation of moderate pressure, toroidal transformer coupled RPS sustained in Ar and Ar/NF₃mixtures. Operation of the RPS in 1 Torr of argon with a power of 1.0 kW at 0.5 MHz and a single core produces a continuous toroidal plasma loop with current continuity being maintained dominantly by conduction current. Operation with dual cores introduces azimuthal asymmetries with local maxima in plasma density. Current continuity is maintained by a mix of conduction and displacement current. Operation in NF₃for the same conditions produces essentially complete NF₃dissociation. Electron depletion as a result of dissociative attachment of NF₃and NF_xfragments significantly alters the discharge topology, confining the electron density to the downstream portion of the source where the NF_xdensity has been lowered by this dissociation. 

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2. Surface oxidation of hydrophobic ZnSe for enhanced growth of atomic layer deposited aluminum oxide

   https://doi.org/10.1116/6.0002018  

   Feit, Corbin; Sosa, Jaynlynn; Kostogiannes, Alexandros; Chazot, Matthieu; Rudawski, Nicholas G.; Jurca, Titel; Richardson, Kathleen A.; Banerjee, Parag (September 2022, Journal of Vacuum Science & Technology A)

   The growth of atomic layer deposited (ALD) Al 2 O 3 on planar ZnSe substrates is studied using in situ spectroscopic ellipsometry. An untreated ZnSe surface requires an incubation period of 27 cycles of ALD Al 2 O 3 before film growth is observed. Pretreating the surface with an ultraviolet generated ozone lowers the incubation to 17 cycles, whereas a plasma-enhanced ALD Al 2 O 3 process can further lower the incubation period to 13 cycles. The use of ozone or plasma-activated oxygen species on ZnSe is found to create ZnO and SeO 2 , which are responsible for converting ZnSe from a hydrophobic to a hydrophilic surface. The interfacial layer between Al 2 O 3 and ZnSe is mapped using high-resolution transmission electron microscopy and scanning transmission electron microscopy/energy dispersive spectroscopy. SeO 2 is volatile and leaves a zinc-rich interface, which is 4.3 nm thick for the ultraviolet generated ozone pretreated sample and 2.5 nm for the plasma-enhanced ALD process. 

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3. Minimum reaction network necessary to describe Ar/CF4 plasma etch

   https://doi.org/10.1117/12.2297502  

   Chopra, Meghali J.; Bonnecaze, Roger T.; Helpert, Sofia (March 2018, Proc. SPIE 10589, Advanced Etch Technology for Nanopatterning VII)

   Predicting the etch and deposition profiles created using plasma processes is challenging due to the complexity of plasma discharges and plasma-surface interactions. Volume-averaged global models allow for efficient prediction of important processing parameters and provide a means to quickly determine the effect of a variety of process inputs on the plasma discharge. However, global models are limited based on simplifying assumptions to describe the chemical reaction network. Here a database of 128 reactions is compiled and their corresponding rate constants collected from 24 sources for an Ar/CF4 plasma using the platform RODEo (Recipe Optimization for Deposition and Etching). Six different reaction sets were tested which employed anywhere from 12 to all 128 reactions to evaluate the impact of the reaction database on particle species densities and electron temperature. Because many the reactions used in our database had conflicting rate constants as reported in literature, we also present a method to deal with those uncertainties when constructing the model which includes weighting each reaction rate and filtering outliers. By analyzing the link between a reaction’s rate constant and its impact on the predicted plasma densities and electron temperatures, we determine the conditions at which a reaction is deemed necessary to the plasma model. The results of this study provide a foundation for determining which minimal set of reactions must be included in the reaction set of the plasma model. 

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4. Plasma-droplet interaction study to assess transport limitations and the role of ^⋅ OH, O ^⋅ ,H ^⋅ ,O ₂ (a ¹ Δ _g ),O ₃ , He(2 ³ S) and Ar(1s ₅ ) in formate decomposition

   https://doi.org/10.1088/1361-6595/ac2676  

   Nayak, Gaurav; Oinuma, Gaku; Yue, Yuanfu; Santos Sousa, João; Bruggeman, Peter J (November 2021, Plasma Sources Science and Technology)

   Abstract Plasmas interacting with liquid microdroplets are gaining momentum due to their ability to significantly enhance the reactivity transfer from the gas phase plasma to the liquid. This is, for example, critically important for efficiently decomposing organic pollutants in water. In this contribution, the role of ⋅ OH as well as non- ⋅ OH-driven chemistry initiated by the activation of small water microdroplets in a controlled environment by diffuse RF glow discharge in He with different gas admixtures (Ar, O 2 and humidified He) at atmospheric pressure is quantified. The effect of short-lived radicals such as O ⋅ and H ⋅ atoms, singlet delta oxygen (O 2 ( a 1 Δ g )), O 3 and metastable atoms of He and Ar, besides ⋅ OH radicals, on the decomposition of formate dissolved in droplets was analyzed using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets. The formate decomposition increased with increasing droplet residence time in the plasma, with ∼70% decomposition occurring within ∼15 ms of the plasma treatment time. The formate oxidation in the droplets is shown to be limited by the gas phase ⋅ OH flux at lower H 2 O concentrations with a significant enhancement in the formate decomposition at the lowest water concentration, attributed to e − /ion-induced reactions. However, the oxidation is diffusion limited in the liquid phase at higher gaseous ⋅ OH concentrations. The formate decomposition in He/O 2 plasma was similar, although with an order of magnitude higher O ⋅ radical density than the ⋅ OH density in the corresponding He/H 2 O plasma. Using a one-dimensional reaction–diffusion model, we showed that O 2 ( a 1 Δ g ) and O 3 did not play a significant role and the decomposition was due to O ⋅ , and possibly ⋅ OH generated in the vapor containing droplet-plasma boundary layer. 

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5. A model-based, Bayesian approach to the CF4/Ar etch of SiO2

   https://doi.org/10.1117/12.2297482  

   Chopra, Meghali J.; Zhu, Xilan; Zhang, Zizhuo Z.; Helpert, Sofia; Verma, Rahul; Bonnecaze, Roger (March 2018, Proc. SPIE 10588, Design-Process-Technology Co-optimization for Manufacturability XII)

   The design and optimization of highly nonlinear and complex processes like plasma etching is challenging and timeconsuming. Significant effort has been devoted to creating plasma profile simulators to facilitate the development of etch recipes. Nevertheless, these simulators are often difficult to use in practice due to the large number of unknown parameters in the plasma discharge and surface kinetics of the etch material, the dependency of the etch rate on the evolving front profile, and the disparate length scales of the system. Here, we expand on the development of a previously published, data informed, Bayesian approach embodied in the platform RODEo (Recipe Optimization for Deposition and Etching). RODEo is used to predict etch rates and etch profiles over a range of powers, pressures, gas flow rates, and gas mixing ratios of an CF4/Ar gas chemistry. Three examples are shown: (1) etch rate predictions of an unknown material “X” using simulated experiments for a CF4/Ar chemistry, (2) etch rate predictions of SiO2 in a Plasma-Therm 790 RIE reactor for a CF4/Ar chemistry, and (3) profile prediction using level set methods. 

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